1. Field of the Invention
The present invention relates to a variable valve operating mechanism of a four-stroke internal combustion engine.
2. Description of Background Art
For a variable valve operating mechanism of a four-stroke internal combustion engine provided including a hydraulically controlled valve pausing mechanism in a valve lifter which is provided between a valve operating cam and a valve stem of a poppet valve, an example is disclosed in Japanese Patent Laid-open Publication No. 2003-27908.
The Japanese Patent Laid-open Publication No. 2003-27908 disclosed the following structure. A slide pin holder is fit and attached in a valve lifter, and a slide pin is fit into the slide pin holder so as to slide in a direction orthogonal to a valve stem. In the slide pin, a stem contact surface abutting on the valve stem of the poppet valve energized by a valve spring and a stem through-hole through which the valve stem penetrates are formed in adjacent to each other. The slide pin is energized by the pin spring in one direction, and oil pressure acts on the slide pin in the opposite direction through an oil pressure supply passage. The slide pin is moved by controlling the oil pressure to cause the stem contact surface and stem through hole to selectively face the valve stem.
Accordingly, when the oil pressure acts to move the slide pin against the pin spring and cause the stem contact surface to face the valve stem, the valve lifter is pressed by the valve operating cam to move, and accordingly, the slide pin presses the valve stem to drive the valve open.
On the other hand, when the oil pressure is released, the slide pin is moved by energizing force of the pin spring to cause the stem through hole to face the valve stem. Even if the valve lifter is pressed by the valve operating cam, therefore, the valve stem penetrates the stem through hole and does not operate, so that the valve is brought into a quiescent state.
In the case where the valve comes into an operating (opening and closing drive) state, when the oil pressure acts on the slide pin, air is released to the opposite side, and the slide pin instantly moves, thus providing a good response. In the case where the valve comes into the quiescent state, however, oil is not actively discharged even if the oil pressure is released. Accordingly, when the oil pressure is not instantly relieved completely, the movement of the slide pin by the spring force of the pin spring is slow, and a desired response cannot be obtained.
Especially in the case of a so-called cylinder quiescent state in which all valves of a cylinder are paused, if the movement of the slide pin is delayed from the release of the oil pressure and the timing of the cylinder to come into the cylinder quiescent state is delayed, fuel feed control becomes difficult to cause fuel to be accumulated or cause pumping loss.